Several lines of pharmacological and genetic evidence support the role of Melanin Concentrating Hormone Receptor-1 (hereafter “MCHR1”) as a modulator of food intake and body weight. Central administration of melanin concentrating hormone (MCH) increases food intake and body weight both in rats and in mice. Chronic ICV infusion of MCH causes increased food intake and ultimately obesity in mice, while infusion of an MCH peptide antagonist blocks MCH-induced food intake and results in weight loss and decreased feeding in diet-induced obese mice.
The expression of both the MCH peptide and receptor are modulated by nutritional status. MCH mRNA is upregulated both in hyperphagic obese mice (ob/ob), and fasted animals. Targeted disruption of the gene for MCH peptide results in hypophagia and leanness. Disruption of the MCHR1 gene causes leanness, altered metabolism, and hyperlocomotion accompanied by mild hyperphagia. Conversely, over-expression of MCH peptide results in hyperphagia, obesity and diabetes. Small molecule MCHR1 antagonists have been shown to cause weight loss in rodent weight and feeding models after both oral and intraperitoneal administration; Eur. J. Pharmacol., 438:129-135 (2002), Nat. Med., 8:825-830 (2002), Eur. J. Pharmacol., 497:41-47 (2004).
Numerous non-peptide MCHR1 antagonists have been disclosed. The scope of the genus for each reflects a common perception regarding the criteria required for ligand recognition as MCHR1 agonists. A recent review of MCHR1 patent disclosures emphasized the commonality of these structures by the following description; “Ubiquitous throughout the MCH patent literature are molecules consisting of a central scaffold to which linkers to an aryl or heteroaryl group and a basic amino functionality are attached.” (Kowalski, T. J. et al., Expert Opin. Investig. Drugs, 13:1113-1122 (2004)). Pharmacophore models of these geni consistently envision a presumed prerequisite electrostatic interaction between a basic amine center of the antagonist ligand and aspartic acid 123 of the receptor which presumably is envisaged to emulate the mandatory interaction between arginine 14 of MCH peptide agonists with aspartic acid 123 of the MCHR1 receptor. (Ulven, T., J. Med. Chem., 48:5684-5697 (2005)) However, incorporation of this basic amine in a MCHR1 antagonist increases substantially the probability of binding to off-target ion-channels and biogenic amine receptors.
In accordance with the present invention, there is provided a series of novel high affinity selective MCHR1 antagonists for which binding affinity is not dependent upon inclusion of a basic amine functionality that is common to most of the disclosed MCHR antagonists. As a consequence, the absence of the basic center greatly reduces the probability of off-target interactions such as binding to other biogenic amine receptors as well as binding to ion channels such as the HERG receptor in the heart. The reduction/abolition of affinity for the HERG receptor is especially important since ligand occupancy is associated with initiation of fatal arrhythmias.